This invention relates to a storage system comprising storage which stores data used by computers in a computer system. In particular, this invention relates to control technology in a storage system comprising storage having means for connecting one or more storage units, and for rendering virtual, as its own device, a device within the connected storage unit.
In recent years there has been explosive growth in the volume of data handled by computers, and as a consequence the capacity of storage unit for storing data is steadily being increased. As a result, storage management costs account for an increasing fraction of system management costs, and the need to lower management costs has become an urgent issue for system operation.
In order to expand storage capacity, new storage may be introduced into an existing computer system comprising a computer (hereafter called a “host”) and storage unit. Two such modes of introduction are conceivable, one in which new large-capacity storage unit is introduced to replace older storage unit, and the other in which the new storage unit is used in conjunction with the older storage unit.
In the case of a mode of introduction in which new storage unit replaces old equipment, all the data within the old storage unit must be transferred to the new storage unit. However, ordinarily the data must be transferred while continuing data input from and output to a host.
Technology to transfer the data of old storage unit to new storage unit, while continuing data input/output with a host, has for example been disclosed in JP-A-10-508967.
Here, the data of a first device of the old storage unit is transferred to a second device allocated to the new storage unit, and the access target from the host is changed from the existing first device to the new second device, so that input/output requests issued from the host to the existing first device are accepted by the new storage unit.
Read requests issued during the transfer are handled by reading from the second device for portions transfer of which has been completed, and by reading from the existing first device for portions transfer of which has not been completed. In the case of write requests, duplicate writing to both the first device and the second device is performed.
In a mode of introduction in which old storage unit and new storage unit are used in conjunction, a mode is possible in which both the new and old storage units are connected directly to the host; but control on the host side is complex.
On the other hand, in for example Japanese Patent Laid-open No. 1-283272, a method is disclosed by which a host accesses a disk of a first storage unit through a second storage unit.
A configuration is employed in which the first storage unit is connected to the second storage unit, disk addresses of the second storage unit are allocated to disks of the first storage unit, and the host also accesses the disks of the first storage unit through the disk control device of the second storage unit.
Upon receiving an input/output request from the host, the second storage unit judges whether the disk being accessed is a disk of the first storage unit or is a disk within the second storage unit, and distributes the input/output request to the access target according to the judgment result.